1. Field of the Invention
This invention relates to multiplexing techniques for controlling operation and obtaining status of a plurality of switching devices disposed along and connected to a single wire bus and, more particularly, in a preferred embodiment to systems for controlling the operations of relay drivers and, in addition, for obtaining status of a series of smart sensors individually connected to a series of indicating, transducing and switching type devices disposed throughout a motor vehicle. The switch status monitoring feature of this invention is similar to the one described in U.S. Pat. No. 4,677,308 by Thomas R. Wroblewski and Frederick O. R. Miesterfeld entitled "Switch Status Monitoring System, Single Wire Bus, Smart Sensor Arrangement Therefor."
2. Description of the Prior Art
A vehicle multiplex system employing a single conductor bus for control signals is described in U.S. Pat. No. 4,370,561 which issued to G. R. Briggs on Jan. 25, 1983. There, a tri-state timing waveform is generated by a multiplex timing unit. A plurality of transmitters and receivers are connected to the single conductor bus. Each transmitter is paired with a corresponding receiver. When it is desired to transmit a control signal to a receiver, a physical command must be applied to the transmitter. The receiver receives the transmitted signal and responds by connecting electrical power from a separate power conductor to a power-operated unit during a specified time in a channel interval assigned to the particular receiver.
Such a system provides control over power-operated units from remote locations, but such a system doesn't provide status information regarding the operation of the transmitters, receivers or of the power operated units.
Another single conductor multiplex system is described in U.S. Pat. No. 4,463,341 which issued July 31, 1984 to S. Iwasaki. There, a single conductor bus is utilized for both power and control function transmission. A plurality of transmitters connected to the bus receive power from the bus and supply control signals to the bus as required. A plurality of receivers also connected to the bus also receive power and control signals from the bus. Each receiver is tuned to respond only to the particular control signal produced by a single transmitter. Upon receipt of the appropriate control signals, the receivers couple power from the bus to various loads. This system requires each transmitter to transmit a unique control signal over the bus that is sensed by a designated receiver. Again control signals are used strictly for controlling circuits in a receiver, the receiver containing circuit means for apply power to a load device. No provisions are provided to monitor the status of the transmitter, receivers or the load devices.